If new iPhones in the shops have ios 8 installed. Will they still have the same gigabytes?

Cause ios 8 takes away 4.1 gigabites and if for example a iPhone 6 with 16 gigabites had ios 8 installed onto it like the rest would it take away some gigabites and when people buy it it would be. 11 gigabytes? I'm 14year old girl saving up for a iPhone 6 and wondering about ios 8 and new phones gigabytes

Why does a 14 year old need a I-Phone?

Since they install it on the phones, it takes up no space. I got an iphone 6 with 16 gigs, and had ios8 with 16 gigs when I started it up.

PS. The update (when you do it at home) doesn't take up gigs, it needs a certain amount to download onto your phone but it doesn't take up space when its done.